The present invention relates to a technology for transferring data stored in a computer system such as the one used as a storage system, and more particularly to a technology for transferring data, stored in a storage system, to a backup system using NAS (Network Attached Storage) and other file system functions.
Today, as the environment of a network such as the Internet evolves and as digital information becomes more diversified (document, drawing, image, visual content, etc.), an information processing system must processes more and more data. The functions of an information processing system that processes a large amount of data are classified roughly into two: the server function and the storage function.
The server function executes applications in a system, which has the server function, to execute application processing provided by the information processing system. The storage function stores data used by a system that has the server function. A system that has the storage function, such as a storage system, has volumes for each system that has the server function such as a file server, with the volumes formatted by a file system recognizable by the file server. The file server and the storage system can be connected by a network called SAN (Storage Area Network). SAN uses a transmission line, usually called a fibre channel, to implement a data transfer method that is faster and more reliable than a general network. Because a plurality of servers and storage systems can be connected via SAN, data can be copied between storage systems without affecting application processing executed by the servers.
Transferring or copying data from a storage system to another storage system or another volume to protect data from an accident, a disaster, or a failure is called “backup”. A server or a storage system to be used for backup may be located at a remote place to which data is transferred or copied via WAN (Wide Area Network).
A server that performs application processing described above and a storage system that stores data used for the application processing are called a primary server and a primary storage system, respectively, while a server and a storage system for backup are called a backup server and a backup storage system, respectively. The backup server and the backup storage system are connected via SAN as with the primary server and the primary storage system.
The servers are connected also to a LAN (Local Area Network), a network separate from the SAN described above. Data is transferred over a LAN using a communication protocol called an IP (Internet Protocol).
In one prior art method, data is transferred from a primary storage system to a backup storage system at backup time via SAN and WAN, one disk block at a time (for example, see JP-A-2002-7304). In the event of a failure on a route via SAN and WAN during data transfer, the data transfer is stopped.
It is also possible that data is transferred from a primary system to a backup system via LAN and WAN using IP. In a general IP-based data transfer using multiple candidates for the transfer route, the network is switched from one network to another if a network failure is detected. Another prior art method transfers data using IP (for example, see JP-A-2001-197112).
A still another prior art method is that the transfer route is selected from multiple networks with different communication protocols (For example, see JP-A-2003-32290).
In the prior art method in which data is backed up via SAN (for example, JP-A-2002-7304), when a failure occurs on a route and data cannot be transferred during the transfer of data from the primary storage system to the backup system via SAN and WAN, the system either waits for the failure on the route to be recovered to restart the data transfer or completes the backup using another route on the SAN and the WAN. In the prior art method in which data is transferred using IP (for example, JP-A-2001-197112), the network route is changed quickly in the IP-based network to avoid a failure. In the prior art method in which data is transferred using the SAN and IP (for example, JP-A-2003-32290), the network can be specified according to the network usage environment.
However, those prior art methods do not assume a data transfer over networks with different transfer protocols or, though it looks as if a data transfer over networks with different transfer protocols is assumed, those prior art methods do not give full consideration to the transfer unit of data that is transferred. Actually, it is necessary to consider the data transfer unit when transferring data between storage systems and, when transferring data between storage systems via SAN using fibre channels, data is transferred on a block basis based on SCSI (Small Computer System Interface). However, when a server transfers data via LAN using IP, the server transfers data in units of files of the file system recognized by the server. Therefore, if a data transfer (in units of blocks) fails on a SAN and WAN route between storage systems, the data cannot be transferred directly between the servers via LAN and WAN. This problem cannot be solved simply by changing the transfer protocol from SCSI to TCP/IP (Transmission Control Protocol/Internet Protocol) but requires consideration for what data transfer unit is to be used. In particular, this problem is important from the aspect of system management when a failure occurs during data transfer on a block basis.